Abstract Magnesium (Mg) is a valuable commodity across many industries, including metals production, transportation, chemical processing, and agriculture. Our oceans effectively represent a limitless source of Mg, and there is subsequently much interest in developing technologies for its recovery in an environmentally sound manner. Herein, we present a new approach to up-concentrate Mg supplies from raw seawater using bismuth (Bi) electrochemistry. Our Bi electrodes can reversibly adsorb and uptake magnesium without deactivation from scale formation. The collected Mg is then released to generate separate MgCl2 product streams with high selectivities over sodium and other seawater constituents. Our approach does not require auxiliary chemical supplies and can continuously increase MgCl2 concentrations from ∼50 to >500 mM by sequentially reusing the concentrated extract from each cycle as the receiving solution for the next. The system demonstrates stable operation for >200 h at consistently low energetics (<600 mV).

The oceans act as a sink for atmospheric CO2, absorbing more than a quarter of global emissions annually. Technologies for marine inorganic carbon dioxide removal (mCDR) have recently gained attention as a means of leveraging this effect to reduce environmental CO2 concentrations. In pH-swing mCDR systems, electrochemical acidification drives the conversion of dissolved inorganic carbon (DIC) in seawater to CO2, which is then removed through vacuum stripping before the water is realkalinized and released to the ocean to draw down atmospheric carbon. While most research has focused on the pH-swing process itself, little attention has been devoted to the stripping step, which is particularly capital- and energy-intensive and indiscriminately removes dissolved oxygen, which is vital to marine life. In this work, we present a framework for an alternative sorbent-mediated CO2 concentration process, analyzing and experimentally demonstrating an electrochemically mediated embodiment. A comparative energetic and technoeconomic assessment is presented, evaluating performance relative to state-of-the-art vacuum processes and indicating that a sorbent-mediated extraction process can be a viable alternative.

Electrochemically mediated sorbent-based carbon capture systems have recently gained attention as an alternative to traditional thermally driven separations. Realizations of such systems typically require a choice between thermodynamically favorable but practically challenging two-stage systems, which combine activation with capture and deactivation with release, or pragmatic but less energy-efficient stepwise four-stage processes decoupling these steps. In this work, we present a thermodynamic assessment of novel multistage systems that are shown to combine the practicality of sequential unit operations with the thermodynamic favorability of concerted operations. A generalized thermodynamic assessment shows that these systems approach the thermodynamic minimum energy of separation in the limit of many stages for an arbitrary sorbent chemistry. Staged desorption is further shown to dramatically decrease the amount of gas in the cell during deactivation, potentially reducing bubble-driven inefficiencies.

In recent years, marine carbon removal technologies have gained attention as a means of reducing greenhouse gas concentrations. One family of these technologies is electrochemical systems, which employ Faradaic reactions to drive alkalinity-swings and enable dissolved inorganic carbon (DIC) removal as gaseous CO2 or as solid minerals. In this work, we develop a thermodynamic framework to estimate upper bounds on performance for Faradaic DIC removal systems. To assess the fundamental mass balances of these systems, we first define unit operations in the DIC/total alkalinity (TA) space. By coupling a seawater speciation model to an electrochemical framework, we provide a generalized comparison of gas evolution and mineralization DIC removal routes, focusing on asymmetric charge/discharge systems. We then show how this framework can be extended to other processes, such as those employing dilution schemes. Finally, we provide a minimum energetic assessment of mCDR pathways relative to direct air capture. Overall, this thermodynamic framework aims to guide system and process design and to drive material discovery and engineering for future electrochemical marine DIC removal systems.

Electrochemical CO2 reduction has emerged as a promising CO2 utilization technology, with Gas Diffusion Electrodes (GDEs) becoming the predominant architecture to maximize performance. GDEs must maintain robust hydrophobicity to prevent flooding, while also ensuring high conductivity to minimize ohmic losses. Intrinsic material tradeoffs have led to two main GDE architectures: carbon paper is highly conductive but floods easily; ePTFE is flooding resistant but non-conductive, limiting electrode sizes to just 5cm2. Here we demonstrate a Hierarchically Conductive GDE architecture (HCGDE) which overcomes these limitations by employing inter-woven microscale conductors within a hydrophobic ePTFE membrane. We develop a model which captures the spatial variability in voltage and product distribution on electrodes due to ohmic losses and use it to rationally design the HCGDE. The HCGDE architecture overcomes scaling limitations, achieving C2+ Faradaic efficiencies of ~75% for electrodes as large as 50cm2. Our approach can be broadly applied to scale any electrode, independent of catalyst chemistry and morphology.

ConspectusThe rising levels of atmospheric CO2 and their resulting impacts on the climate have necessitated the urgent development of effective carbon capture technologies. Electrochemical carbon capture systems have emerged as a potential alternative to conventional thermal systems based on amine solutions due to their modularity, energy efficiency, and lower environmental impact. Among these, aqueous electrochemical pH swing systems that capitalize on the pH dependence of dissolved inorganic carbon (CO2/HCO3-/CO32-) speciation to capture and release CO2 are of particular interest as they can be flexible in system design and in the range of electrochemical potentials used as well as being environmentally benign. In this Account, we present our recent findings in pH swing-based electrochemical carbon capture using redox-active materials, paving the way toward a sustainable solution for mitigating CO2 emissions.In the first section, we discuss the utilization of molecular redox-active organic materials in electrochemical carbon capture by the pH swing method. This electrochemical system configuration involves homogeneous aqueous electrolytes containing molecular redox-active compounds combined with inert carbon-based electrodes. We first present the development of redox-active amine and oxygen-insensitive neutral red (NR)-based systems. Notably, the discovery of 1-aminopyridinium (1-AP) as an electrochemically reversible compound enables efficient pH swing, leading to an impressive electron utilization of 1.25 mol of CO2 per mole of electrons. Additionally, we explore an oxygen-insensitive neutral red/leuconeutral red (NR/NRH2) redox system, which demonstrates potential applicability to direct air capture (DAC) systems with ambient air as a feed gas.The second section focuses on the utilization of inorganic nanomaterials for redox-active electrodes for pH swing-based electrochemical carbon capture. In this system configuration, we employ redox-active electrodes for inducing reversible pH swings in aqueous electrolytes without interrupting other ionic species, except protons. Specifically, we explore the effectiveness of manganese oxide (MnO2) electrodes for achieving selective CO2 removal from simulated flue gas. We then demonstrate a bismuth/silver (Bi/BiOCl, Ag/AgCl) nanoparticle electrode system as a sodium-insensitive pH swing system for extracting dissolved inorganic carbon (DIC) from simulated seawater with high electrochemical energy efficiency.Overall, these advances in pH swing-based electrochemical carbon capture offer promising preliminary solutions for combating climate change by capturing CO2 from dilute sources such as flue gas and ambient air as well as enabling direct carbon removal from ocean water. While these systems have demonstrated impressive energy efficiency and environmental benefits using redox-active materials, they represent only the beginning of our research journey. Further development and optimization are currently underway as we strive to unlock their full potential for large-scale implementation, paving the way toward a sustainable and carbon-neutral future.

CO 2 is removed from oceanwater acidified during chloride-mediated electrochemically modulated reaction of bismuth electrodes.

Molten alkali metal borates have recently shown promise as high-temperature sorbents for capture of CO 2 and acid gases. These molten salt sorbents enable realization of thermodynamic enhancements offered by conventional solid high temperature sorbents while resolving practical challenges such as morphological degradation. Prior studies have focused on regeneration of alkali borates through steam sweeping and thermal cycling. In this work, we demonstrate that mixed sodium-lithium borate salts as CO 2 sorbents can also be regenerated electrochemically, producing valuable multiwalled carbon nanotubes (MWCNT) via electroreduction of captured CO 2 . Effects of cathode materials and operating conditions in CO 2 electroreduction in molten sodium-lithium borate are quantified. By varying relative starting compositions of alkali borates and alkali carbonates, an optimal composition of borates and carbonates is determined, achieving high coulombic efficiencies and significantly higher CO 2 uptake capacities than traditionally employed carbonate salts used for conversion of CO 2 into CNTs in the desirable 550-650°C range.

Surface plastics and microplastics commingled with biomass are emerging pollutants in the marine environment.

As the concentration of carbon dioxide is continuously increasing, there have been a lot of efforts to remove CO2 from various sources. While most of the attention has been focused on CO2capture at point sources followed by geological storage, interest in negative emission strategies also increased recently. One of the promising approaches for negative emissions is removing CO2 from ocean water. The world ocean is the largest carbon sink, containing 120 times higher concentration compared to the atmosphere. Therefore, by removing CO2 from ocean water, we can expect a reduction in CO2 concentration in the atmosphere. Considering that the CO2-reduced oceanwater should be returned to the ocean, the addition of chemicals, and the formation of undesirable compounds should be avoided. In this respect, the electrochemical approach can be a good choice because it does not require additional chemicals, and the control of voltage can tune the reactions in the system. Until now, several approaches have been made by using the electrodialysis process. However, the use of bipolar membrane for water dissociation makes this process expensive, making the application of this process sluggish. In this talk, we will present a new membrane-free approach based on electrochemical modulation of the pH to release the CO2 from ocean water. After removing CO2, the treated water is alkalized before being returned to the ocean. Using an electrochemical pH swing approach, we could successfully remove the CO2 from ocean water without employing expensive membrane or additional chemicals.

A family of blended compositions of molten mixed lithium and sodium borate (Li1.5Na1.5BO3) and eutectic lithium-potassium carbonate (Li1.24K0.76CO3) salts has been introduced as reversible carbon dioxide absorbents and as media for CO2 electrolysis for carbon conversion. Material properties, temperature effects and kinetics of CO2 uptake were examined. Li, Na borate can absorb up to 7.3 mmol g-1 CO2 at 600 °C. The blended borate-carbonate compositions are molten in the 550-600 °C temperature range, with viscosity adjustable to within a 10-1000 Pa s window depending on the borate/carbonate ratio. The blends can withstand cyclic temperature and CO2 pressure swings without significant deterioration of their CO2 uptake capabilities. Addition of eutectic carbonate into mixed Li, Na borate salts lowers overall CO2 uptake due to the lower solubility of CO2 in carbonate. However, addition of the eutectic lowers the temperature of the pressure swing operation and dramatically accelerates the CO2 uptake during the initial stage of the absorption, potentially enabling a faster cycling. Electroreduction of CO2 and carbon deposition on a galvanized steel cathode was more effective with increasing carbonate fraction in the molten alkali borate/carbonate blend. Blended borate/carbonate compositions with 50-60% borate content possessed sufficiently high loading capacity for CO2 and simultaneously enabled maximum carbon product yield and Coulombic efficiency. Most of the recovered carbon product was shown to be in the form of multiwalled carbon nanotube.

Focused laser spike (FLaSk) dewetting employs a localized heat source to create thermocapillary-induced trench-ridge morphologies. Using a universal heating substrate coupled with optical microscopy, we have studied the dewetted ridge feature for several distinct thin films of glass-forming materials. The evolution of the ridge’s radius over time can be modeled to derive a maximum dewetted radius and a characteristic decay time. The decay time shows an Arrhenius behavior when compared to the mean melt pool temperature, leading to a characteristic activation energy. An effective viscosity can also be defined. These descriptors demonstrate FLaSk’s potential for rapid metrology.

Dynamic spatial light modulators (SLMs) are capable of precisely modulating a beam of light by tuning the phase or intensity of an array of pixels in parallel. They can be utilized in applications ranging from image projection to beam front aberration and microscopic particle manipulation with optical tweezers. However, conventional dynamic SLMs are typically incompatible with high-power sources, as they contain easily damaged optically absorbing components. To address this, we present an SLM that utilizes a viscous film with a local thickness controlled via thermocapillary dewetting. The film is reflowable and can cycle through different patterns, representing, to the best of our knowledge, the first steps towards a dynamic optical device based on the thermocapillary dewetting mechanism.

Focused laser spike (FLaSk) dewetting employs a localized heat source to create thermocapillary induced trench-ridge morphologies. By using a universal heating substrate to create a material independent thermal profile coupled with optical microscopy, we have studied the dewetted ridge feature for several distinct glassy thin films. The evolution of the ridge's radius over time can be modeled using stretched exponential functions to derive a maximum dewetted radius and a characteristic decay time. The characteristic decay time shows a super-Arrhenius behavior resembling viscosity change during the glass transition process. An effective viscosity is defined by balancing the thermocapillary Marangoni stress using the mean temperature in the melt pool, indicating clear signature of composition. In this way, we have demonstrated that FLaSk dewetting as a rheologymethod can be employed for high-throughput analysis of glassy thin film materials at high temperature and shear.

This paper describes the development and optimization of a conceptual thermal management system for electrified aircraft. Here, a vertical takeoff and landing (VTOL) vehicle is analyzed with the following electrically sourced heat loads considered: motors, generators, rectifiers, and inverters. The vehicle will employ liquid-cooling techniques in order to acquire, transport, and reject waste heat from the vehicle. The purpose of this paper is to threefold: (1) Present a potential modeling framework for system level thermal management system simulation, (2) Analyze typical system characteristics, and (3) Perform optimization on a system developed for a specific vehicle to minimize weight gain, power utilization, and drag. Additionally, the paper will study the design process, specifically investigating the differences between steady state and transient sizing, comparing simulation techniques with a lower fidelity option and quantifying expected error.

Thermocapillary dewetting of liquids and molten films has recently emerged as a viable alternative to conventional microprocessing methods. As this thermal gradient-induced mechanism is universal, it can be applied to any material. This work explores the sequential dewetting of materials with varying melting points, including polymers and metals, to create aligned morphologies. The variation in melting point allows for the dewetting of single layers at a time or mobility-limited simultaneous dewetting. As a result, a variety of multimaterial structures can be produced with built-in alignment, such as arrays of concentric circles, lines with periodic segmentation, or islands on holes. This approach employs photothermal methods to induce the necessary thermal gradient. manipulating several variables in order to influence the consequent structures. Adjusting laser power and light intensity allows for the control of temperature for selective dewetting of films; altering beam size and exposure time affects the extent of dewetting in terms of diameter size; overlap effects and simultaneous dewetting can result in complex architectures. This controlled writing of patterns also presents a technique to create both masks at low temperatures for conductive multilayers as well as templates for electrospray deposition.

Focused laser spike (FLaSk) excitation has been demonstrated as a reliable technique for the patterning of micro-to-nanoscale features locally by thermocapillary shear of thin films. Recent work on polymer thin films has revealed that, overlapping laser scans can leverage coupled thermal and fluid effects to create subwavelength patterns. Compared to polymeric films, metallic thin films possess both a lower melt viscosity and higher surface tension. Here, we investigate overlapping effects in the dewetting of, similar to 15 nm gold thin films on borosilicate and quartz glass continuous wave laser. During this process, FLaSk initiates capillary and thermocapillary dewetting simultaneously. Further, the low oxidation potential and high vapor pressure of gold lead to nonequilibrium vaporization during heating. Since the parameters of overlapping scans control the amount of material that is heated and to what temperature it is heated, selection of laser power, scanning distance, writing speed, and numerical aperture results in particles with different sizes and spacing deposited on the writing substrates or a positioned superstrate through a laser-induced localized physical vapor deposition (LILPVD) process. If the laser parameters are selected within a specific working range, uniform or periodic particle distributions can be repeatably deposited in this fashion, which can then be used as seeds for nanomaterial growth. In addition, if the substrate melts during FLaSk, the viscous force of the liquid-on-liquid dewetting broadens the range of patterning conditions by resisting the motion of the gold leading to more uniform particles over a large range of parameters.

Electrospray processing utilizes the balance of electrostatic forces and surface tension within a charged spray to produce charged microdroplets with a narrow dispersion in size. In electrospray deposition, each droplet carries a small quantity of suspended material to a target substrate. Past electrospray deposition results fall into two major categories: (1) continuous spray of films onto conducting substrates and (2) spray of isolated droplets onto insulating substrates. A crossover regime, or a self-limited spray, has only been limitedly observed in the spray of insulating materials onto conductive substrates. In such sprays, a limiting thickness emerges, where the accumulation of charge repels further spray. In this study, we examined the parametric spray of several glassy polymers to both categorize past electrospray deposition results and uncover the critical parameters for thickness-limited sprays. The key parameters for determining the limiting thickness were (1) field strength and (2) spray temperature, related to (i) the necessary repulsive field and (ii) the ability for the deposited materials to swell in the carrier solvent vapor and redistribute charge. These control mechanisms can be applied to the uniform or controllably-varied microscale coating of complex three-dimensional objects.